Is my JWT token secure with this decoder?

Absolutely. All string splitting, base64url decoding, and JSON parsing operations occur entirely client-side using JavaScript inside your browser. No token payloads, credentials, or keys are ever sent across the network.

Can this tool verify JWT signatures?

This tool splits and displays the signature section and warns if the signature part is completely missing. However, verifying cryptographic signatures requires you to input a secret key or public certificate, which we advise against doing on online tools to avoid key leakage.

What do standard claims like exp, iat, and sub mean?

These are RFC 7519 registered claims: "sub" (Subject) identifies the user/entity, "iss" (Issuer) identifies the auth server, "aud" (Audience) defines intended recipients, "exp" (Expiration Time) marks when the token becomes invalid, and "iat" (Issued At) details when the token was created.

Why does the tool show a security warning for "alg": "none"?

The "none" algorithm indicates that the JWT is unsecured and contains no signature verification. Accepting tokens with "alg: none" makes systems highly vulnerable to spoofing and privilege escalation attacks.

Is my JWT sent to a server for decoding?

No, decoding is performed entirely client-side in your browser using JavaScript. Your token and its details are never sent over the network.

JWT Decoder - Decode JSON Web Tokens Online

JWT Decoder

Decode JWT tokens online to view header, payload, and signature, check expiration, and verify claims — everything runs locally in your browser.

Claim name	JSON key	Extracted parameter value
Subject	sub	-
Issuer	iss	-
Audience	aud	-
Expiration Time	exp	-
Issued At	iat	-
Not Before	nbf	-
Algorithm	alg (Header)	-
Token Type	typ (Header)	-

Claim name

JSON key

Extracted parameter value

Subject

sub

Issuer

iss

Audience

aud

Expiration Time

exp

Issued At

iat

Not Before

nbf

Algorithm

alg (Header)

Token Type

typ (Header)

What Is a JSON Web Token (JWT)?

A JSON Web Token (JWT) is a compact, URL-safe way to represent claims (statements about a user or session) that need to be passed between two parties. JWTs allow applications to authenticate users without storing session data on the server, since all required identity and authorization information can travel inside the token itself, which is why they are so common in modern APIs and microservices.

The Three-Part Structure of Every JWT

Every JWT is made up of three segments joined by dots: header.payload.signature. The header describes metadata like the signing algorithm, the payload carries the actual claims (such as sub, iss, or exp), and the signature is a cryptographic value used to detect tampering. Each of the first two segments is Base64URL-encoded JSON, not encrypted, so anyone can read it.

What This JWT Decoder Actually Does

This JWT decoder splits a pasted token into its three segments and Base64URL-decodes the header and payload so you can read their JSON contents in plain text. It does not perform cryptographic signature verification, because that requires the secret or private key used to sign the token, which never leaves the issuing server and is not something a decoder tool has access to.

Decoding a Token Is Not the Same as Validating It

Being able to read a JWT's claims does not mean the token is genuine or unaltered. A tampered or expired token can still be decoded perfectly fine, so any real authorization decision must be made server-side by verifying the signature with the correct key, not by trusting whatever a decoded-but-unverified payload happens to say.

Common Payload Claims Explained

Most JWTs include a handful of registered claims: iss identifies who issued the token, sub identifies the subject (usually a user ID), aud names the intended audience, iat records when the token was issued, and exp records when it expires. Recognizing these claims makes it much easier to understand what a token is actually asserting.

Practical Use Case: Debugging a Rejected API Call

A very common reason an API call suddenly starts returning 401 Unauthorized is a token that has quietly expired. Pasting the JWT into this decoder and checking the exp claim against the current time lets you confirm in seconds whether expiration is the culprit, without adding any logging or debugging code to your application.

Your Token Stays in Your Browser

This JWT decoder runs entirely client-side in JavaScript and never sends the pasted token to any server for processing, so it is safe to use for debugging tokens from your own applications. As a general habit, still avoid pasting real production JWTs containing sensitive claims into any online tool if you are unsure how it handles input.

Encoded Token (JWT)

Awaiting Token

Decoded segments

Token Claims & Security Metadata

Recent JWT Drafts

Understanding JWT Tokens & Security

What Is a JSON Web Token (JWT)?

The Three-Part Structure of Every JWT

What This JWT Decoder Actually Does

Decoding a Token Is Not the Same as Validating It

Common Payload Claims Explained

Practical Use Case: Debugging a Rejected API Call

Your Token Stays in Your Browser

Questions, answered

Related guides

MD5 vs SHA-256: Which Hash Algorithm Should You Use and Why

JSON to CSV Conversion: When and How to Convert Structured Data Correctly

Blood Pressure Chart by Age: What Your Numbers Actually Mean

BMI for Indians: Why the Standard BMI Chart Is Misleading for South Asians

Recommended for Your Workflow

JSON Formatter

SQL Formatter

CSS Minifier

JavaScript Minifier

More from Developer Tools

Color Picker

JSON to CSV Converter

JSON Validator

CSV to JSON Converter

Recently Used Tools

Popular Tools on EasyToolio

SIP Calculator

Salary Calculator

Compound Interest Calculator

GST Calculator

What do you need to work out next?

Enjoying JWT Decoder?